Branch Maintenance

You may have noticed by now that Subversion is extremely
flexible. Because it implements branches and tags with the same
underlying mechanism (directory copies), and because branches
and tags appear in normal filesystem space, many people find
Subversion intimidating. It's almost too
flexible. In this section, we'll offer some suggestions for
arranging and managing your data over time.

Repository Layout

There are some standard, recommended ways to organize a
repository. Most people create a trunk
directory to hold the “main line” of development,
a branches directory to contain branch
copies, and a tags directory to contain
tag copies. If a repository holds only one project,
often people create these top-level directories:

Of course, you're free to ignore these common layouts.
You can create any sort of variation, whatever works best for
you or your team. Remember that whatever you choose, it's not
a permanent commitment. You can reorganize your repository at
any time. Because branches and tags are ordinary directories,
the svn move command can move or rename
them however you wish. Switching from one layout to another
is just a matter of issuing a series of server-side moves; if
you don't like the way things are organized in the repository,
just juggle the directories around.

Remember, though, that while moving directories may be
easy to do, you need to be considerate of your users as well.
Your juggling can be disorienting to users with existing
working copies. If a user has a working copy of a particular
repository directory, your svn move
operation might remove the path from the latest revision.
When the user next runs svn update, she will
be told that her working copy represents a path that no
longer exists, and the user will be forced to svn
switch to the new location.

Data Lifetimes

Another nice feature of Subversion's model is that
branches and tags can have finite lifetimes, just like any
other versioned item. For example, suppose you eventually
finish all your work on your personal branch of the
calc project. After merging all of your
changes back into /calc/trunk, there's
no need for your private branch directory to stick around
anymore:

And now your branch is gone. Of course, it's not really
gone: the directory is simply missing from the
HEAD revision, no longer distracting
anyone. If you use svn checkout,
svn switch, or svn list
to examine an earlier revision, you'll still be able to see
your old branch.

If browsing your deleted directory isn't enough, you can
always bring it back. Resurrecting data is very easy in
Subversion. If there's a deleted directory (or file) that
you'd like to bring back into HEAD, simply
use svn copy to copy it from the old
revision:

In our example, your personal branch had a relatively
short lifetime: you may have created it to fix a bug or
implement a new feature. When your task is done, so is the
branch. In software development, though, it's also common to
have two “main” branches running side by side for
very long periods. For example, suppose it's time to release
a stable version of the calc project to the
public, and you know it's going to take a couple of months to
shake bugs out of the software. You don't want people to add
new features to the project, but you don't want to tell all
developers to stop programming either. So instead, you create
a “stable” branch of the software that won't
change much:

And now developers are free to continue adding
cutting-edge (or experimental) features to
/calc/trunk, and you can declare a
project policy that only bug fixes are to be committed to
/calc/branches/stable-1.0. That is, as
people continue to work on the trunk, a human selectively
ports bug fixes over to the stable branch. Even after the
stable branch has shipped, you'll probably continue to
maintain the branch for a long time—that is, as long
as you continue to support that release for customers. We'll
discuss this more in the next section.

You are reading Version Control with Subversion (for Subversion 1.6), by Ben Collins-Sussman, Brian W. Fitzpatrick, and C. Michael Pilato.
This work is licensed under the Creative Commons Attribution License v2.0.
To submit comments, corrections, or other contributions to the text, please visit http://www.svnbook.com/.